1. Field of Invention
The present invention relates to a data processing system and operating method. More particularly, the present invention relates to a data processing system and operating method that facilitates the maintenance of a set of uniform reference layers among a central processing unit, a control chip and a printed circuit board.
2. Description of Related Art
FIG. 1 is a schematic diagram showing a conventional signal transmission wiring system between a central processing unit 100, a north bridge 200 and a printed circuit board (PCB) 300. As shown in FIG. 1, the central processing unit 100 includes a chip 102 and a substrate having a stack structure 106. The stack structure 106 within the central processing unit 100 includes, from top to bottom, a signal layer 108, a ground layer 110, a power source layer 112 and a signal layer 114. The north bridge 200 or the printed circuit board 300 respectively has its own substrate that further including associated stack structure. The stack structure within the north bridge 200 includes, from top to bottom, a signal layer 206, a power source layer 208, a ground layer 210 and a signal layer 212. Similarly, the stack structure within the printed circuit board 300 includes, from top to bottom, a signal layer 302, a power source layer 304, a ground layer 306 and a signal layer 308. The north bridge 200 further includes a chip 201 above the substrate 202.
According to FIG. 1, the signal layer 212 of the north bridge 200 and the signal layer 114 of the central processing unit 100 are adjacent to the signal layer 302 of the printed circuit board 300. Due to wiring layout, electrical signals going out from the central processing unit 100 may be transmitted to the north bridge 200 via any one of the signal layers (such as the signal layer 108 or the signal layer 114) of the central processing unit 100. The north bridge 200 may use any one of the signal layers (such as the signal layer 206 or the signal layer 212) to receive or to respond. The printed circuit board 300 serves as a signal transmission interface between the central processing unit 100 and the north bridge 200. When the central processing unit 100 issues an electrical signal, any one of the signal layers (such as the signal layer 302 or the signal layer 308) within the printed circuit board 300 may be selected to conduct the signal transmission.
Although the aforementioned wiring layout dispenses with the need to route electrical signals within a particular signal layer to a specific signal layer, such a design often lead to an increase in the probability of corruption of the electrical signal along the transmission route. For most devices, such conditions may not cause any unexpected side effect to the electrical signals. However, the central processing unit 100 and the north bridge 200 are both fast and voluminous signal transmitters, and most transmissions involve critical signals including address signals, data signals and strobe signals. Hence, any minor deterioration of signal quality may seriously affect the operation of the entire system.
In addition, a circuit path is created whenever signals are transmitted from the central processing unit 100 to the control chip 200 or vice versa. The circuit path includes a return path that is often referred to as a reference layer. The return path may be a ground layer such as 110, 306 or 210 (represented by dash line in FIG. 1) or the return path may be a power source layer such as 112, 304 and 208. Everything depends on whether the transmitted signal follows the first signal layer such as 108, 302, 206 or the second signal layer such as 114, 308, 212. A signal usually selects a return path closest to the signal transmission layer and having the smallest resistance. Hence, if the signal chooses the first signal layer, the ground layer is used as a reference layer to form the return path. On the other hand, if the signal chooses the second signal layer, the power source layer is used as a reference layer to form the return path.
The constituent pathway of the return path may directly affect the quality of the signal transmission. Signal timing may be less stable if the return path is a power source layer rather than a reference ground layer. The power source layer provides a less stable return effect because the power source layer also serves as a voltage source for driving other devices.
The aforementioned printed circuit board has four layers. In practice, the total number of layers in a printed circuit board stack may be as many as 6 to 9. Hence, the actual cost of producing of a printed circuit board is much higher than the one illustrated.